Though the key was pressed, nothing ______ on the screen.
A:appeared
B:was appeared
C:appears
D:is appeared
I'm going to learn_______the violin. ( )
如图所示为《唐书》所载830名进士的出身分布比例,由此可见,唐代科举制( )
下列关于禽流感病毒的叙述,错误的是( )